Abstract
Thermogravimetric TG and a single riser from an industrial 4.3 m coke oven were used as pyrolysis reactors to systematically study the newly developed pyrolysis treatment of desulfurization wastewater. The TG study showed that the mixed salt in the desulfurization wastewater was transformed into the crystalline form of ammonium thiocyanate (in the temperature range 95.87-127.38 °C), followed by the isomerization of ammonium thiocyanate to thiourea (in the temperature range 127.38-246.26 °C), involving a total of five major stages. The final pyrolysis temperature was 540 °C, and the cumulative weight loss was 99.57%. The study on the single riser from an industrial 4.3 m coke oven showed that the relationship between the spray amount of desulfurization wastewater (v), the temperature drop (ΔT) and the concentration of ammonium thiocyanate (c) in the coke-oven raw gas at the outlet of the rising pipe were respectively ΔT = -2.939v and c = f(v). The maximum desulfurization wastewater treatment capacity of the 4.3 m single riser was 61.98 kg h(-1). The spraying optimization conditions were: spraying position, 3 m from the water seal cap of the riser; spraying amount, 50-55 L h(-1); spraying time, from 10 min after the coal loading to less than 20 h during the coking process. An industrial test device for treating 12 000 tons of desulfurization wastewater was constructed, which then ran normally, with the new technology for treating the high concentration polluted wastewater-desulfurization wastewater formed.